4 Aspects to Consider When Buying LED Outdoor Light Fixtures

There are many LED products in the market, but far from all of them are of good quality. It’s true, when choosing which type of lighting to use, there are actually many aspects to consider and a right decision will often get twice the result with half the effort. Low-quality LED lights may flicker or not turn on at all. They may have serious light decay and short lifespan, which not only affects illumination, but also fails to yield any energy-saving results.

In the following section, we will discuss the requirements that high-quality LED lights should meet. We will look at four aspects: power sources; the optical material of lamps; the heat sinks and outer shells of lamps; and chip encapsulation technology.

Aspect 1: Power Supply

Data shows that 52% of all outdoor LED malfunctions are caused by power supply failure or instability (see figure).

The application environment of outdoor LED lighting is very complex, and extreme weather conditions frequently cause malfunctions. At the same time, the voltage stability of outdoor power lines is usually very different to that of indoor electrical wires. Because of this, the requirements for the reliability of outdoor power source drivers are much more stringent.

Lightning resistance capability: It probably doesn’t come as a surprise to anyone that lightning strikes can be extremely harmful to power supplies. The most harmful lightning strikes can produce voltages of 4KV or more.

Lightning resistance capacity criteria are based on IEC-61000-4-5, the main indicators being that differential resistance should be 2KV and common-mode resistance should be 4KV.

Extreme temperature resistance capability: In some parts of the world, outside temperatures can be as high as 50℃, and cold temperatures might reach as low as -30℃. This requires power supplies to be operational within a wide range of working temperatures.

Water resistance capability: The difference between ‘rainproof’ and ‘waterproof’ is not just one word: the words actually indicate very different protective capacities. ‘Rainproof’-grade only requires IP65, while ‘waterproof’-grade requires IP67. This means that a power supply is safe to use, even if submerged in water, and internal PCB circuit boards and other components will not be affected by moisture or salt spray. A power supply graded as IP67 is enough to resist malfunction caused by moisture and respiration effect in salty and foggy environment.

Aspect 2: The Optical Materials

The lighting quality of a lighting fixture is directly affected by the choice of optical materials. In general, glass is the best material to use for lampshades, since it is transparent, easy to clean, and does not age. However, it is important to use tempered glass, since normal glass may shatter and potentially cause a security risk. If the lampshade is made of plastic, the best option is to select UV resistant material. This reduces the risk of yellowing, ageing, or the lampshade becoming brittle after long periods of use. It is worth noting thathigh transmittance is not always the best choice, the back sides also need to be noticed.

Aspect 3: Capabilities of Heat Sink and Shell

Outdoor conditions vary, there is a great deal of complexity and unpredictability. The heat sink and outer shell are very important components of outdoor LED lighting fixtures, and one needs to take into account several aspects, such as protective and heat dissipation capacities, mechanical strength, installation methods, and structural design. First, let’s make it clear why outdoor lighting requires more on heat sink and shell than indoor lighting.

7 Major Challenges to Outdoor LED Lighting

High temperatures: High outdoor temperatures may cause the working temperature of the lighting fixture to rise, causing components to age, power supplies to malfunction, and LED lights to decay and break.

Extreme low temperature: Low temperatures may inflict stress on the surface of the lighting fixture, causing the outer shell to crack. Low temperatures may also cause the adaptability of the lighting driver to decrease.

Corrosive environments: Snow, coastal salt-rich air, the immediate environment of chemical plants, soil acidification and erosion may cause the outer shell of the lighting fixture to corrode or crack, causing it to decrease in strength or stop functioning entirely.

Ultraviolet rays: Ultraviolet sun rays may cause the optical components of lighting fixtures to age or become brittle.

Damage from humans or animals: Animals may climb on to the fixtures, or humans might intentionally damage them.

To deal with all these possible challenges, the outdoor LED light body and heat sink should possess following capabilities:

Water and dust protective capacity: IP is the international code used to determine the protective grade of a lighting fixture. The IP grade is composed of two digits: the first digit indicates how well the fixture can resist dust; the second indicates how well the fixture can resist water. A high number indicates a higher protective grade. For safety reasons, all live components must be isolated in order to prevent electric shocks.

Heat dissipation capacity: The main way of cooling outdoor lighting fixtures is by natural convection dissipation. In order to increase the dissipation area, the heat sinks are usually made into the shape of fins. The heat dissipation of the fixture itself may directly affect the stability and quality of LED lights.

Mechanical strength: Since outdoor lighting fixtures are more exposed than indoor lighting, a certain amount of mechanical strength (such as thick supporting frames and strong linking components) is necessary to increase reliability.

Installation flexibility: Good lighting fixtures should be easy to install, regardless where they are installed. This allows for a flexible installation process and reduced installation costs.

Self-cleaning capability: A self-cleaning structure of LED light is a sure indication of good design. The surfaces of outdoor lighting fixtures are often covered by debris, such as dust, leaves, and bird droppings (or even bird carcasses!). If these objects cannot be effectively removed, may cause the protective layer of paint to corrode, and the effective heat dissipating area of the heat sink may decrease. A heat sink with a self-cleaning design can make use of wind and rain water to effectively clean and flush away debris, ensuring the continued normal operation of the LED light.

Aspect 4: Suitable LED Light Source

High power LED diodes: In order to balance the need for high power and small size in outdoor lighting fixtures, currently most LED lights (mainly street lights) make use of 1W or stronger LED lights arranged in multiple rows, and are assembled through parallel connection (such as SMD3030, SMD2835, SMD3535 etc. are common). However, the thermal resistance of this method is relatively high, and it puts high requirements on the design and manufacturing process of the heat sink.

High power LED Array/ COB: This type of LED uses 30W, 50W, 100W or even larger arrays. The light emitting portion of this type of package is relatively compact, and is easy to fit for lenses or reflectors, enabling better control of light distribution. High power LED arrays on today’s market usually use epoxy resin or silica gel for encapsulation. Epoxy-encapsulated packages have rather poor temperature resistance, and will age with time; silica-encapsulated packages are much better, but also more expensive. Arrays should use copper substrates in order to facilitate connection with external heat sinks. The surfaces of the two components need to be very smooth and covered in thermal conducive silicone grease. This ensures that heat can be quickly transmitted from the copper substrate to the external heat sink.

Medium-low power adhesive packages: Adhesive light sources make use of large amounts of small chips to replace high power chip packages. The benefit of this design is that it takes full advantage of the size of the lighting fixture’s heat sink. Its efficiency is higher since it does not concentrate heat to the center, but disperses it instead. The thermal resistance of this package is minimal, and it is very good for heat dissipation. However, because a large amount of low power diodes is distributed over a larger area, it is not useful for settings that require concentrated lighting, but it is common in tri-proof lights and fluorescent lights, and usually used in combination with diffusing lampshades, producing well-distributed, scattered light rays.